Flow soldering can easily be justified as the single most important process in the manufacturing of printed wiring assemblies. If the flow solder process is not adequately controlled, a large number of touch-up operators have to be employed to rework the defects of the flow solder process. The flow solder process in most cases is operator dependent, therefore the challenge is how to gain better control of the flow solder process.
There are other computer controlled flow solder machines, but these computers automate the machine, not the process. For example, they control the solder immersion depth by simply changing the solder pump speed. This method ruins the wave profile in which great care was used to obtain the optimum wave profile, where the solder just falls off the backgate of the solder pot.
To reduce solder defects, control of the flux applied to the circuit board is critical, and control of the flux application is critical. It has been found that not only should flux be applied to the etch side of the printed circuit board by a flux wave, but flux defects are greatly reduced by applying flux to the topside by use of top side flux guns. Also critical to the flow solder process is the preheating of the printed circuit board. Preheating of the printed circuit board is done to drive off the carrier solvent of the flux, to reduce thermal shock, and to activate the flux. It is important that the preheat be consistent and controlled so that repeatable results can be obtained.
To have overall good soldering, the speed of travel of the printed circuit board, the amount of flux applied, the amount of preheat, the depth into the solder wave by the circuit board, and the dwell time of the board in the solder wave all must be considered and correlated to ensure proper soldering of the circuit board. In prior flow solder machines, the parameters are set manually and not necessarily changed for each board type, or the machine is automated, but not the process.